Latex coatings are finding greater usage because of ease of application/cleanup, increasingly restrictive emission regulations, and moderate costs. However, when high performance protection is required, such as abrasion resistance, latex systems are often inadequate and epoxy and polyurethane coatings must be used. These systems are considerably more expensive to purchase and apply than are latex systems, and also have greater hazards associated with worker exposure during application. Accordingly, there is presently a need for latex coatings with enhanced abrasion resistance. Past attempts to improve abrasion resistance of latex systems have involved using polymers with greater inherent strength, such as acrylics, and also making higher molecular weight polymers.
High molecular weight polyethylene (HMW PE) has outstanding abrasion resistance properties, thereby making it the material of choice for high abrasion applications, such as mining equipment, pillow blocks, wear strips, and gears. One problem associated with HMW PE is that it is difficult to fabricate into end products partially because it is not a typical thermoplastic material due to its high molecular weight. One method for making products consists of sintering HMW PE resin into solid blocks using heat and pressure which are then machined to form end products. This process is very time consuming, requires significant labor, and generates much scrap. Another method for forming HMW PE end products is by ram extrusion which is used primarily for making profiles and in which the productivity is measured in inches per hour.
A second problem associated with HMW PE is its high coefficent of thermal expansion, relative to metal. Hence, when sheets of HMW PE are clad to steel surfaces, as in protective liners for ore ships, hopper cars, and truck beds, provisions must be made to accommodate relative growth and shrinkage. Attempts to solve problems associated with attaching HMW PE to metal surfaces generally involve using many fasteners in small sheets. Recently, a mounting system was developed which consists of bolts through slotted grooves in the HMW PE sheets. These areas, in turn, have to be protected with HMW PE cover strips. In any case, installation is a time consuming and expensive process.
Attempts to solve problems associated with fabricating HMW PE end products have primarily involved blending-in lower molecular weight PE or adding softening agents in order to enable thermoplastic processing techniques to be used. These approaches have had only limited success, and they result in compromising physical performance properties. Adding other plastics with HMW PE to form a composite having a unique combination of physIcal properties is one potential solution to the above problems. In the past such composites have been produced by mechanically combining or chemically bonding two or more polymers. For example, acrylonitrilebutadiene-styrene terpolymer is produced by grafting polyacrylonitrile (a rigid polymer) onto polystyrene-butadiene (an elastic polymer). A common method for physically combining two materials into a composite is by blending. In this manner, for example, there is produced a blended composite of polybutylene terephthalate with polycarbonate (a very rigid material). The known chemical methods of making composite polymers require very precise control of processing conditions in order to produce products of desired uniform characteristics. The available physical alternatives, on the other hand, require good compatibility among the constituent materials to avoid phase separation, which limits the choice of polymers which can be thus combined with one another. This virtually rules out blends of highly elastomeric materials with rigid plastics because, most often, these are incompatible.
U.S. Pat. No. 4,692,470 discloses a method of incorporating finely divided polymeric solid particles into viscous liquids by incorporating a wetting agent which is effective for displacing absorbed air from the surface, crevices and pores of the particles thereby allowing better wetting and incorporation of the particles into the viscous liquids.
An article by H. Schonhorn, et al. entitled "Surface Treatment of Polymers. II Effectiveness of Fluorination as a Surface Treatment for Polyethylene" J. App. P. Sci., Vol. 12 pp 1231-1237 (1968), discloses an effective surface treatment for adhesive bonding of polyethylene. The surface treatment disclosed involves exposing the polymer to an environment of gaseous fluorine such as fluorine diluted in argon. It is disclosed that treatment of the polymer with elemental fluorine most likely effectively eliminates the weak boundary layer associated with polyethylene by either cross-linking or by increasing the molecular weight in the surface region.
U.S. Pat. No. 4,009,304 discloses a process for improving the adhesion of polyester yarn, tire cord or fabric in polyester reinforced rubber goods, such as tires, by fluorinating the polyester yarn, tire cord or fabric prior to incorporating such into the tire or rubber goods. Additionally, U.S. Pat. No. 3,940,520 teaches a process for improving the water wicking and moisture transport properties of synthetic resins, such as polyolefins, by contacting said resins to a gaseous reaction medium containing elemental fluorine and sulfur dioxide.